Rotorcraft are called on to operate in a wide variety of environments and under conditions that may be extreme, so the turbine engine(s) of a rotorcraft must be protected in order to withstand such conditions.
Firstly, during takeoff, the blast from the lift rotor of the rotorcraft can raise dust, and even gravel, from the ground, so it is essential to protect the air intake of the rotorcraft turbine engine(s) to prevent ingestion of the above-mentioned elements. Thereafter, it is necessary to eliminate particles that are in suspension in the air being absorbed by the turbine engines of the rotorcraft, particularly if the rotorcraft is used in sandy regions where the air is saturated with particles of sand.
Secondly, rotorcraft can be called on to fly under so-called “icing” conditions. During this type of flight, ice can obstruct the air intake of a turbine engine of the rotorcraft, in part or even completely, thereby leading to a significant or even total drop in the power delivered by the engine. Similarly, ice can be ingested by the engine, and such ice is then liable severely to disturb the operation of the engine or to damage it.
Consequently, in order to be able to fly under particular conditions, i.e. in atmospheres laden with particles or ice, for example, it is appropriate to protect the engine(s) of the aircraft, and in particular the air intake(s) thereof in order to guarantee good performance of the engine.
Similarly, it can be appropriate to ensure that the engine does not ingest birds, where such ingestion can be very destructive, e.g. breaking the blades of the turbine compressor.
Aircraft manufacturers have therefore designed devices for protecting the air intakes of turbine engines so as to prevent such engines ingesting particles. The term “particle” is used for convenience to cover birds, which means that in the text below, the term “particle” could be understood as designating any element present in the air and liable to damage the engine.
Document WO 2007/090011 discloses a first filter system including flexible filter means arranged in a frame having two side borders.
The flexibility of the borders of the frame and of the filter means enables the filter system to be deformed so as to be fitted on an aircraft.
Nevertheless, that first filter system is not controllable, with the filtering power of the system remaining constant, ignoring natural degradation due to the filter means becoming obstructed while in use. However, it can be advantageous to be able to control this filtering power, e.g. for the purpose of reducing it to its minimum in the event of the filter means becoming clogged.
If the filter means become clogged, the engine will no longer be fed with air, and that will cause it to stop and possibly lead to a catastrophic situation.
Similarly, document U.S. Pat. No. 5,674,303 describes a second filter system that is not controllable.
That second filter system comprises a casing having an inside surface that defines a passage in which filter means are arranged.
In addition, a flexible seal is placed between the inside surface of the casing and the filter means. The flexible seal enables the filter means to move in the fluid flow direction along the passage under the influence of vibration, if any.
Consequently, that second filter system is well adapted to combat potentially destructive vibration, but it does not include any means enabling its filtering power to be adjusted.
Document GB 853 646 describes a third filter system arranged in the air passage of an air intake of a turbine engine.
That third filter system includes filter means arranged within a fairing. In operation, the fairing moves in translation so as to enable the filter means to be deployed.
Although effective, that third filter means presents the drawback of obstructing a large fraction of the air passage, thereby limiting the flow rate of air delivered to the engine.
In addition, since the deployment of the filter means is not capable of being modulated, the filtering power of the filter system can either be zero or at its maximum.
Finally, Document DE 2 213 352 proposes a fourth filter system for protecting a turbine engine against ingesting birds.
Filter means, specifically a broad endless link constituted by a trellis, is set into motion by rollers rotating about respective axes of rotation, driven by drive means.
In addition, a portion of the filter means is located upstream from a turbine engine.
The trellis of the filter means has two orifices, and when the two orifices are in register with each other in said portion, the incident air passes through the orifices of the filter means and reaches the turbine engine. This incident air is therefore not filtered.
In contrast, using the rollers, it is possible to offset the orifices relative to each other. The incident air then passes through the trellis of the filter means prior to reaching the engine.
Nevertheless, it is found that the fourth system is particularly bulky. In addition, the friction that exists between the rollers and the filter means is large and therefore damaging, thereby considerably limiting its lifetime.
In addition, that fourth filter system is designed to prevent elements of relatively large size being ingested, namely birds, and the filter means does not appear to be capable of being modulated, the filtering power of the filter system then being either zero or at its maximum.